Acute and chronic myeloid leukemias are responsible for approximately 15,000 deaths in the USA every year. These diseases frequently afflict people in the prime of their lives, and substantially less than half of all achieve long-term remission with current therapies, Most treatment options are both intense and toxic, requiring anti-neoplastic poly-chemotherapy, and, in some cases, therapy as radical as allogeneic hematopoietic cell transplantation, with its attendant risks. The overall goal of this proposal is to develop differentiation therapy to supplement the treatment regimens for this group of diseases. We will focus on the identification of the most effective analogs (deltanoids) of the physiological form of vitamin D, 1,25- dihydroxyvitamin D3 (1,25D3) administered at low concentrations to leukemia cells in culture to study alterations in gene expression and other changes in cell physiology. The deltanoids and 1,25D3 will also be administered in combination with nontoxic substances currently used as food preservatives or additives, or with potential for such use, to maximize the differentiation activity of the deltanoids. Established lines of leukemia as well as samples of leukemic cells freshly obtained from patients will be used for studies of cell differentiation. Insight into differentiation control will be obtained by examination of signaling pathways with particular attention to MAPK pathways and into cell cycle regulation by the expression of cyclin-dependent kinases as well as their activators and inhibitors. This will be accomplished by adding pharmacological agents, antisense oligonucleotides, transcription factor decoys, and transfected plasmid constructs to study the molecular consequences of these manipulations, which will be determined by immunoblotting, Northern analysis, RT-PCR, coimmunoprecipitation, and other standard techniques. Differentiating cells will be monitored by determination of surface makers as well as the activity of various kinases as and as their expression. The information obtained in basic studies will be utilized to guide development of a new generation of deltanoids and deltanoid combinations with co-inducers, while translational studies on leukemic cells ex vivo will serve to identify subgroups of myeloid leukemias most suitable for the initiation of clinical trials.